Our goal is to identify and characterize functions present in the terminus region of the Escherichia coli chromosome that are important for coordinating chromosome replication with cell division. Particular emphasis will be placed on characterization of the sites within the terminus region which inhibit replication forks. Specifically, it is proposed to: 1) Locate the exact sites where clockwise and counterclockwise replication forks are inhibited in the E. coli chromosome. 2) Develop a plasmid system in which the replication blocks are functional to facilitate further study of these sites. 3) Clone and sequence the replication blocks for comparison with each other and with termination sites from other replicons. 4) Use in vitro or in vivo systems to study the mechanism of replication fork inhibition. 5) Study the phenotype of bacterial strains in which combinations of the replication blocks and various other parts of the terminus region have been deleted. The goal is to identify the regions which, when deleted, cause improper segregation of daughter chromosomes, filamentation, and loss of coordination between chromosome replication and cell division. These experiments will provide fundamental information about the control of bacterial growth and division. Information of this type can be readily applied to new approaches for combating bacterial disease.